1. Field of the Invention
The present invention relates to an aluminum conductor composite core (ACCC) reinforced cable and method of manufacture. More particularly, the present invention relates to a cable for providing electrical power having a composite core, formed by fiber reinforcements and a matrix, surrounded by aluminum conductor capable of carrying increased ampacity and operating at elevated temperatures.
2. Description of the Related Art
In a traditional aluminum conductor steel reinforced cable (ACSR) the aluminum conductor transmits the power and the steel core is designed to carry the transfer load. Conductor cables are constrained by the inherent physical characteristics of the components; these components limit ampacity. Ampacity is a measure of the ability to send power through the cable. Increased current or power on the cable causes a corresponding increase in the conductor's operating temperature. Excessive heat will cause the cable to sag below permissible levels. Typical ACSR cables can be operated at temperatures up to 100° C. on a continuous basis without any significant change in the conductor's physical properties related to sag. Above 100° C., ACSR cables suffer from thermal expansion and a reduction in tensile strength. These physical changes create excessive line sage. Such line sag has been identified as one of the possible causes of the power blackout in the Northeastern United States in 2003. The temperature limits constrain the electrical load rating of a typical 230-kV line, strung with 795 kcmil ACSR “Drake” conductor, to about 400 MVA, corresponding to a current of 1000 A. Therefore, to increase the load carrying capacity of transmission cables, the cable itself must be designed using components having inherent properties that allow for increased ampacity without inducing excessive line sag.
Although ampacity gains can be obtained by increasing the conductor area that surrounds the steel core of the transmission cable, increasing conductor volume increases the weight of the cable and contributes to sag. Moreover, the increased weight requires the cable to use increased tension in the cable support infrastructure. Such large weight increases typically would require structural reinforcement or replacement of the electrical transmission towers and utility poles. Such infrastructure modifications are typically not financially feasible. Thus, there is financial motivation to increase the load capacity on electrical transmission cables while using the existing transmission structures and liens.
Prior art applications disclose a composite core comprised of a single type of glass fiber and thermoplastic resin. The object is to provide an electrical transmission cable which utilizes a reinforced plastic composite core as a load bearing element in the cable and to provide a method of carrying electrical current through an electrical transmission cable which utilizes an inner reinforced plastic core. The composite core fails in these objectives. A one fiber system comprising glass fiber does not have the required stiffness to attract transfer load and keep the cable from sagging. Secondly, a composite core comprising glass fiber and thermoplastic resin does not meet the operating temperatures required for increased ampacity, namely, between 90° C. and 230° C.
Physical properties of composite cores are further limited by processing methods. Previous processing methods cannot achieve a high fiber to resin ratio by volume or weight. These processes do not allow for creation of a fiber rich core that will achieve the strength required for electrical cables. Moreover, the processing speed of previous processing methods is limited by inherent characteristics of the process itself. For example, traditional pultrusion dies are approximately 36 inches long, having a constant cross section. The longer dies create increased friction between the composite and the die slowing processing time. The processing times in such systems for epoxy resins range from about 3 inches/minute to about 12 inches/minute. Processing speeds using polyester and vinyl ester resins can produce composites at up to 72 inches/minute. With thousands of miles of cables needed, these slow processing speeds fail to meet the need in a financially acceptable manner.
It is therefore desirable to design an economically feasible cable that facilitates increased ampacity without corresponding cable sag. It is further desirable to process composite cores using a process that allows configuration and tuning of the composite cores during processing and allows for processing at speeds up to 60 ft/min.